1. Field of the Invention
The present invention relates to a magnetic transfer method of magnetically transferring a predetermined data such as servo data or the like, and in particular to a method of performing magnetic transfer to a high-density magnetic recording medium.
2. Description of the Related Art
Generally speaking, with regard to magnetic storage mediums, there is a demand for increased storage capacity and low cost. Further desired are so-called high-speed access mediums, which are capable of advantageously reading out the data of a specified location in a short time. At present, a new type of magnetic recording medium, which comprises two magnetic layers separated by a coupling layer formed of ruthenium, utilizing antiferromagnetic coupling (AFC) to realize an remarkable increase in recording capacity is being developed. This new media type is sometimes referred to as a “Synthetic Ferromagnetic Media” (SF media). AFC media are characterized by each of the magnetic layers having respectively opposite magnetization directions, by providing a nonmagnetic coupling layer between the two magnetic layers. Examples of high-density magnetic recording mediums in which the thermal stability of the antiferromagnetic coupling between two magnetic layers can be improved and the recording density further increased have been proposed in Japanese Unexamined Patent Publication Nos. 2001-56921, 2001-56922, and 2001-56925.
With regard to this type of high-density magnetic recording medium, so-called tracking servo technology, wherein the magnetic head accurately scans the track width to achieve a high S/N ratio, is utilized in the same method as for the magnetic recording mediums such as the conventional hard disks or flexible disks used in ZIP (Iomega) drives or the like.
The servo data required to implement the tracking servo technology must be “preformatted”, that is, recorded on the disk in advance when the disk is manufactured. At present, a preformat such as that described above employs a specialized servo recording apparatus, and is formed by causing the magnetic head to approach the disk, and writing the signal one track at a time while the disk is being rotated. Because the servo data is recorded for one disk at a time, on one track at a time, a significant amount of time is required for the preformatting operation, giving rise to a problem with respect to the manufacturing efficiency.
Further, although the magnetic data of the AFC media is recorded and reproduced by scanning the track thereof with a magnetic head in the same method as for conventional magnetic recording media, because the size of the magnetic head is relatively large in comparison to a magnetization region, a magnetic field producing noise on the inverse magnetization portions is inadvertently applied thereto. Still further, because the magnetic field is applied not only to the upper magnetic layer but also to the lower layer of the two magnetic layers, there is a limit to the recording accuracy of the AFC media due to problems such as the disorder caused in the magnetization state of the lower magnetic layer; therefore, a reproduction signal having a favorable S/N ratio cannot be obtained therefrom. A favorable servo reproduction signal must be obtained in order to accurately control the track position. If the S/N ratio of the servo reproduction signal of a servo signal that has been preformatted by use of a servo recording apparatus is not favorable, such a situation becomes an obstacle to the performance of a favorable tracking servo function.
An accurate and efficient preformatting method, wherein a pattern bearing servo data, which has been formed on a master medium, is magnetically transferred to a magnetic recording medium, has been proposed in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566.
According to these magnetic transfer technologies, a master medium having an uneven pattern corresponding to the data that is to be transferred to a magnetic recording medium (a slave medium) is prepared. By bringing this master medium into close contact with a slave medium to form a conjoined body, and applying a transfer magnetic field thereto, a magnetic pattern corresponding to the data (e.g., a servo signal) borne on the master medium is transferred to the slave medium. The preformatting can be performed without changing the relative positions of the master medium and the slave medium that is, while the two media remain relatively static. Therefore not only is it possible to perform an accurate recording of the preformat data, it becomes possible to advantageously do so in an extremely short time. Accordingly, it can be considered that this method is applicable in transferring a magnetic pattern to AFC media, also.
There has been proposed, as described in Japanese Patent Application No. 11(1999)-117800, an extremely favorable magnetic transfer method of transferring data to a conventional magnetic recording medium, comprising the steps of subjecting the magnetic layer of a slave medium to an initial magnetization process in advance, and then applying a transfer magnetic field to the slave medium, which has been conjoined with a master medium, in the direction opposite that of the initial magnetization.
However, the magnetic transfer methods proposed thus far have presumed that the transfer would be performed to a conventional single magnetic layer; the performance of a transfer to an AFC media with an antiferromagnetic magnetically coupling two layers, has not been considered. Because the structure of a conventional magnetic recording medium and the AFC medium are different, if a conventional magnetic transfer method is employed to perform a magnetic transfer to an AFC medium, an accurate, favorable transfer is not obtained; therefore, there is a demand for a magnetic transfer method to the properties of AFC media.